﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;


static class SubstringForStringBuilder
{

    public static StringBuilder Substring(this StringBuilder str, int startIndex, int length)
    {
        string substring = str.ToString().Substring(startIndex, length);
        return new StringBuilder(substring);
    }

    public static StringBuilder Substring(this StringBuilder str, int startIndex)
    {
        string substring = str.ToString().Substring(startIndex);
        return new StringBuilder(substring);
    }
}

